1. Field of the Invention
The present invention relates to the technology of data transmission and reception between control units through a serial bus, and in particular to a method and an apparatus for serial data communication which is capable of accurate data transmission and reception regardless of a change in circumstances by performing a two-way communication between two independent communication control units, processing a task independently by the one control unit when communication is disabled due to an abnormality of the other control unit.
2. Description of the Prior Art
In the conventional serial data transmission technology, data transmission and reception is performed under the control of a master control unit. In other words, when the data transmission and reception is performed between two control units, a clock is controlled by one master control unit. Accordingly, a slave control unit transmits and receives data in accordance with the clock which is controlled by the master control unit.
FIG. 1 and FIG. 3 illustrate normal data and transformation data which are on a bus in the conventional serial data transmission technology. FIG. 1 illustrates an example of an IM bus protocol developed by ITT, FIG. 1a illustrates normal data transmission, FIG. 1b illustrates data transformation influenced by the surrounding noise. Herein, the surrounding noise may be generated by an external symbol dictionary (ESD) or internal discharge of a color picture tube (CPT), and a signal for producing contrast 36hex data may be transformed into the signal for making contrast 16hex data due to the surrounding noise.
FIG. 2 illustrates an example of a Philips 12C bus protocol which has been used widely in recent years. FIG. 2a illustrates a normal data transmission, and FIG. 2b illustrates data transformation influenced by the surrounding noise. Data adjustment by a tuner may be considered as a countermeasure for such data transformation, but data from the other control unit may be changed due to the data adjustment by the tuner. On the 12C bus, although it is possible to check whether the slave control unit has received the data as a byte unit, an incorrect operation may be performed when the data is changed.
FIG. 3 illustrates a master control unit in a clock line occupation state or in a long communication pause state during the data transmission. At this time the slave control unit cannot perform independently.
The conventional technology has the following problems. When transmitted data from the master control unit is damaged due to the surrounding noise, the slave control unit may process the data without recognizing the damage and may perform an inaccurate operation. When the master control unit stops the data reception while receiving the data, in other words, when the master control unit holds the clock line due to its abnormality, the slave control unit cannot perform any operation. When there is a need to get information from the master control unit or to transmit information from the slave control unit, it is difficult to get the information independently without the process operation of the master control unit.